That's definitely all there is to it.
If there's no PA support for the bass, there isn't any for the drums, either.
Doesn't matter what size room, or how many people are in it. All you need is enough rig to keep up with the acoustic output of the drums.
(Actually, the same applies even with full PA support.)
Yup - I make sure I have enough rig to balance volumes with the drums and guitars on stage - anything above that gets taken care of by the PA...
- georgestrings